crash on removing an instrument from a score

See http://musescore.org/en/node/45246, there is a score that causes this crash on deleting staff #6

b98f097

stack trace:
0 Ms::ChordRest::undoUnlink chordrest.cpp 125 0x7f4050
1 Ms::Chord::undoUnlink chord.cpp 279 0x7d0343
2 Ms::Measure::cmdRemoveStaves measure.cpp 1044 0x774815
3 Ms::Score::undoRemoveStaff undo.cpp 785 0x71b6c1
4 Ms::Score::cmdRemoveStaff score.cpp 2470 0x72ff2e
5 Ms::Score::cmdRemovePart score.cpp 2291 0x72f32f
6 Ms::MuseScore::editInstrList instrdialog.cpp 255 0x44798f
7 Ms::MuseScore::cmd musescore.cpp 3889 0x47b36d
8 Ms::MuseScore::cmd musescore.cpp 3812 0x47ae36
9 Ms::MuseScore::qt_static_metacall moc_musescore.cpp 809 0x403911
10 ZN11QMetaObject8activateEP7QObjectiiPPv ...\MuseScore\win32install\bin\Qt5Core.dll 0x68a64351
11 ZN12QActionGroup7hoveredEP7QAction ...\MuseScore\win32install\bin\Qt5Widgets.dll 0x61dc4b95
12 ?? 0x27ea1c30
13 ZN7QAction8activateENS_11ActionEventE ...\MuseScore\win32install\bin\Qt5Widgets.dll 0x61dc3b6e
14 ?? 0x28cd78
15 ?? 0x24748b04
16 ?? 0x74f68510
17 ?? 0x89068b28
18 ?? 0xfff189cb
19 OpenComponentLibraryOnMemEx C:\Windows\syswow64\clbcatq.dll 0x74d83910
...